The present invention relates to a new and distinctive celery (Apium graveolens var. dulce) variety, designated ADS-4. There are numerous steps in the development of any novel, desirable plant germplasm. Plant breeding begins with the analysis and definition of problems and weaknesses of the current germplasm, the establishment of program goals, and the definition of specific breeding objectives. The next step is selection of germplasm that possess the traits to meet the program goals. The goal is to combine in a single variety or hybrid an improved combination of desirable traits from the parental germplasm. These important traits may include increased stalk size and weight, higher seed yield, improved color, resistance to diseases and insects, tolerance to drought and heat, and better agronomic quality.
Practically speaking, all cultivated forms of celery belong to the species Apium graveolens var. dulce that is grown for its edible stalk. As a crop, celery is grown commercially wherever environmental conditions permit the production of an economically viable yield. In the United States, the principal growing regions are California, Florida, Texas and Michigan. Fresh celery is available in the United States year-round although the greatest supply is from November through January. For planting purposes, the celery season is typically divided into two seasons, summer and winter, with Florida, Texas and the southern California areas harvesting from November to July, and Michigan and northern California harvesting from July to October. Fresh celery is consumed as fresh, raw product and occasionally as a cooked vegetable.
Celery is a cool-season biennial that grows best from 60° to 65° F. (16° to 18° C.), but will tolerate temperatures from 45° to 75° F. (7° to 24° C.). Freezing will damage mature celery by splitting the petioles or causing the skin to peal, making the stalks unmarketable. This is an occasional problem in plantings in the winter regions. However, celery can tolerate minor freezes early in the crop.
The two main growing regions for celery (Apium graveolens L.) in California are located along the Pacific Ocean: the central coast or summer production area (Monterey, San Benito, Santa Cruz and San Luis Obispo Counties) and the south coast or winter production area (Ventura and Santa Barbara Counties). A minor region (winter) is located in the southern deserts (Riverside and Imperial Counties).
In the south coast, celery is transplanted from early August to April for harvest from November to mid-July; in the Santa Maria area, celery is transplantaed from January to August for harvest from April through December. In the central coast, fields are transplanted from March to September for harvest from late June to late December. In the southern deserts, fields are transplanted in late August for harvest in January.
Commonly used celery varieties for coastal production include Tall Utah 52–75, Conquistador and Sonora. Some shippers use their own proprietary varieties. Celery seed is very small and difficult to germinate. All commercial celery is planted as greenhouse-grown transplants. Celery grown from transplants is more uniform than from seed and takes less time to grow the crop in the field. Transplanted celery is placed in double rows on 40-inch (100-cm) beds with plants spaced between 6.7 and 7 inches (22.5-cm) apart.
Celery is an allogamous biennial crop. Celery consists of 11 chromosomes. Its high degree of out-crossing is accomplished by insects and wind pollination. Pollinators visiting celery flowers include a large number of wasp, bee and fly species. Celery is subject to inbreeding depression, which appears to be genotype dependent, since some lines are able to withstand continuous selfing for three or four generations. Crossing of inbreds results in heterotic hybrids that are vigorous and taller than sib-mated or inbred lines.
Celery flowers are protandrous, with pollen being released 3–6 days before stigma receptivity. At the time of stigma receptivity the stamens will have fallen and the two stigmata unfolded in an upright position. The degree of protandy varies, which makes it difficult to perform reliable hybridization, due to the possibility of accidental selfing.
Celery flowers are very small, significantly precluding easy removal of individual anthers. Furthermore, different developmental stages of the flowers in umbels makes it difficult to avoid uncontrolled pollinations. The standard hybridization technique in celery consists of selecting flower buds of the same size and eliminating the older and younger flowers. Then, the umbellets are covered with glycine paper bags for a 5–10 day period, during which the stigmas become receptive. At the time the flowers are receptive, available pollen or umbellets shedding pollen from selected male parents are rubbed on to the stigmas of the female parent.
Plants require a period of vernalization while in the vegetative phase in order to induce seed stalk development. A period of 6–10 weeks at 5–8° C. is usually adequate. However, unless plants are beyond a juvenile state or a minimum of 4 weeks old they may not be receptive to vernalization. Due to a wide range of response to the cold treatment, it is often difficult to synchronize crossing, since plants will flower at different times. However, pollen can be stored for 6–8 months at −10° C. in the presence of silica gel or calcium chloride with a viability decline of only 20–40%, thus providing flexibility to perform crosses over a longer time.
For selfing, the plant or selected umbels are caged in cloth bags. These are shaken several times during the day to promote pollen release. Houseflies (Musca domestics) can also be introduced weekly into the bags to perform pollinations.
Choice of breeding or selection methods depends on the mode of plant reproduction, the heritability of the trait(s) being improved, and the type of cultivar used commercially (e.g., F1 hybrid cultivar, pureline cultivar, etc.). For highly heritable traits, a choice of superior individual plants evaluated at a single location will be effective, whereas for traits with low heritability, selection should be based on mean values obtained from replicated evaluations of families of related plants. Popular selection methods commonly include pedigree selection, modified pedigree selection, mass selection, and recurrent selection.
The complexity of inheritance influences choice of the breeding method. Backcross breeding is used to transfer one or a few favorable genes for a highly heritable trait into a desirable cultivar. This approach has been used extensively for breeding disease-resistant cultivars. Various recurrent selection techniques are used to improve quantitatively inherited traits controlled by numerous genes. The use of recurrent selection in self-pollinating crops depends on the ease of pollination, the frequency of successful hybrids from each pollination, and the number of hybrid offspring from each successful cross.
Each breeding program should include a periodic, objective evaluation of the efficiency of the breeding procedure. Evaluation criteria vary depending on the goal and objectives, but should include gain from selection per year based on comparisons to an appropriate standard, overall value of the advanced breeding lines, and number of successful cultivars produced per unit of input (e.g., per year, per dollar expended, etc.).
Promising advanced breeding lines are thoroughly tested and compared to appropriate standards in environments representative of the commercial target area(s) for three years at least. The best lines are candidates for new commercial cultivars; those still deficient in a few traits are used as parents to produce new populations for further selection.
These processes, which lead to the final step of marketing and distribution, usually take from ten to twenty years from the time the first cross or selection is made. Therefore, development of new cultivars is a time-consuming process that requires precise forward planning, efficient use of resources, and a minimum of changes in direction.
A most difficult task is the identification of individuals that are genetically superior, because for most traits the true genotypic value is masked by other confounding plant traits or environmental factors. One method of identifying a superior plant is to observe its performance relative to other experimental plants and to a widely grown standard cultivar. If a single observation is inconclusive, replicated observations provide a better estimate of its genetic worth.
The goal of plant breeding is to develop new, unique and superior celery cultivars. The breeder initially selects and crosses two or more parental lines, followed by repeated selfing and selection, producing many new genetic combinations. The breeder can theoretically generate billions of different genetic combinations via crossing, selfing and mutations. The breeder has no direct control at the cellular level. Therefore, two breeders will never develop the same line, or even very similar lines, having the same celery traits.
Each year, the plant breeder selects the germplasm to advance to the next generation. This germplasm is grown under unique and different geographical, climatic and soil conditions, and further selections are then made, during and at the end of the growing season. The cultivars that are developed are unpredictable. This unpredictability is because the breeder's selection occurs in unique environments, with no control at the DNA level (using conventional breeding procedures), and with millions of different possible genetic combinations being generated. A breeder of ordinary skill in the art cannot predict the final resulting lines he develops, except possibly in a very gross and general fashion. The same breeder cannot produce the same line twice by using the exact same original parents and the same selection techniques. This unpredictability results in the expenditure of large research monies to develop superior celery cultivars.
The development of commercial celery cultivars requires the development of celery varieties, the crossing of these varieties, and the evaluation of the crosses. Pedigree breeding and recurrent selection breeding methods are used to develop cultivars from breeding populations. Breeding programs combine desirable traits from two or more varieties or various broad-based sources into breeding pools from which cultivars are developed by selfing and selection of desired phenotypes. The new cultivars are crossed with other varieties and the hybrids from these crosses are evaluated to determine which have commercial potential.
Pedigree breeding is used commonly for the improvement of self-pollinating crops or inbred lines of cross-pollinating crops. Two parents which possess favorable, complementary traits, are crossed to produce an F1. An F2 population is produced by selfing one or several F1's or by intercrossing two F1's (sib mating). Selection of the best individuals is usually begun in the F2 population; then, beginning in the F3, the best individuals in the best families are selected. Replicated testing of families, or hybrid combinations involving individuals of these families, often follows in the F4 generation to improve the effectiveness of selection for traits with low heritability. At an advanced stage of inbreeding (i.e., F6 and F7), the best lines or mixtures of phenotypically similar lines are tested for potential release as new cultivars.
Mass and recurrent selections can be used to improve populations of either self- or cross-pollinating crops. A genetically variable population of heterozygous individuals is either identified or created by intercrossing several different parents. The best plants are selected based on individual superiority, outstanding progeny, or excellent combining ability. The selected plants are intercrossed to produce a new population in which further cycles of selection are continued.
Backcross breeding has been used to transfer genes for a simply inherited, highly heritable trait into a desirable homozygous cultivar or line that is the recurrent parent. The source of the trait to be transferred is called the donor parent. The resulting plant is expected to have the attributes of the recurrent parent (e.g., cultivar) and the desirable trait transferred from the donor parent. After the initial cross, individuals possessing the phenotype of the donor parent are selected and repeatedly crossed (backcrossed) to the recurrent parent. The resulting plant is expected to have the attributes of the recurrent parent (e.g., cultivar) and the desirable trait transferred from the donor parent.
The single-seed descent procedure in the strict sense refers to planting a segregating population, harvesting a sample of one seed per plant, and using the one-seed sample to plant the next generation. When the population has been advanced from the F2 to the desired level of inbreeding, the plants from which lines are derived will each trace to different F2 individuals. The number of plants in a population declines each generation due to failure of some seeds to germinate or some plants to produce at least one seed. As a result, not all of the F2 plants originally sampled in the population, will be represented by a progeny when generation advance is completed.
Descriptions of other breeding methods that are commonly used for different traits and crops can be found in one of several reference books (e.g., “Principles of Plant Breeding” John Wiley and Son, pp. 115–161, 1960; Allard, 1960; Simmonds, 1979; Sneep et al., 1979; Fehr, 1987; “Carrots and Related Vegetable Umbelliferae”, Rubatzky, V. E., et al., 1999).
Proper testing should detect any major faults and establish the level of superiority or improvement over current cultivars. In addition to showing superior performance, there must be a demand for a new cultivar that is compatible with industry standards or which creates a new market. The introduction of a new cultivar will incur additional costs to the seed producer, the grower, processor and consumer; for special advertising and marketing, altered seed and commercial production practices, and new product utilization. The testing preceding release of a new cultivar should take into consideration research and development costs as well as technical superiority of the final cultivar. For seed-propagated cultivars, it must be feasible to produce seed easily and economically.
Celery in general is an important and valuable vegetable crop. Thus, a continuing goal of plant breeders is to develop stable, high yielding celery cultivars that are agronomically sound. The reasons for this goal are obviously to maximize the amount of yield produced on the land. To accomplish this goal, the celery breeder must select and develop celery plants that have the traits that result in superior cultivars.